Epidemiological and experimental lines of evidence support the concept that dietary fat reduction may prevent breast cancer in postmenopausal patients by reducing circulating levels of estradiol which may in turn reduce breast tumor growth. The primary source of estradiol after menopause is estrone derived from androstenedione by aromization in peripheral tissues. Upper body obesity, a common condition after menopause, is associated with an increased risk for breast cancer as well as increased circulating levels of estradiol resulting from increased aromatization. Reducing caloric intake, reducing fat intake and increasing fiber intake have all been shown to reduce circulating estradiol levels.